Optimized structure of tubular thermoelectric generators using n-type Bi2Te3 and p-type Sb2Te3 thin films on flexible substrate for energy harvesting

Abstract Thermoelectric energy harvesting has garnered considerable interest as a means of power supply in Internet of Things sensors. In this study, tubular thin-film thermoelectric generators (TTTEGs) were developed using flexible thermoelectric films for energy harvesting. The strip-shaped n-type Bi2Te3 and p-type Sb2Te3 thin films were deposited on a polyimide sheet using radio-frequency magnetron sputtering, followed by thermal annealing. After the formation of metal electrodes to connect p-n pairs, the flexible thin-film generator was rolled and placed in a plastic tube. Assuming that the TTTEGs would be partially immersed in hot water in the optimal design, the temperature distributions in the TTTEGs were calculated using computational fluid dynamics. The calculations indicated that a steep temperature gradient occurred near the water surface, which was also observed in an experimental measurement. Therefore, we prepared TTTEGs with different film lengths ranging from 16 to 36 mm while the film width and radius of tube were maintained at 2 mm and 7.5 mm, respectively. The TTTEGs with a film length of 16 mm exhibited the highest thermoelectric performance, i.e., an open-circuit voltage of 122.9 mV and a maximum output power of 306.8 nW, at a temperature difference of 20 K. This trend occurred because the short-film TTTEG effectively utilized the steep temperature gradient and had a small circuit resistance.